Syngas, a mixture of carbon monoxide and hydrogen is a versatile feedstock for the methanol, ammonia and Fischer-Trospch synthesis processes and also for production of hydrogen. It is conventionally produced by various forms of steam reforming e.g. methane steam reforming (MSR). Although technologically very well established and practiced commercially since a long, the steam reforming is highly endothermic and hence highly energy intensive process and also has high capital and process operating costs. Under the present energy crisis, there is a need to replace the steam reforming by a more economical process, particularly requiring a little or no external energy.
Process for the reforming of hydrocarbons to syngas, such as autothermal reforming (ATR) and catalytic partial oxidation (CPO) of hydrocarbon(s), involving exothermic hydrocarbon conversion reactions and hence requiring little or no external energy, are also known in the prior art.
In the ATR process, the conversion of hydrocarbon(s) to syngas is accomplished in two steps as follows: In the first step, only part of hydrocarbon is combusted by oxygen in flame, producing a hot stream comprising uncombusted hydrocarbon(s), steam and carbon oxides; the temperature of this stream is above about 1300° C. In the second step, the hot stream is contacted with a steam reforming catalyst to convert the uncombusted hydrocarbon(s) to syngas by the steam and CO2 reforming reactions. In this process, the catalyst subjected to a very high temperature, above about 1300° C. and hence it is deactivated due to sintering at the high temperature. Moreover, the catalyst is also subjected to high temperature shocks during the start up and closing down operations in the autothermal reforming leading to catalyst fouling, which results from both the disintrigration and sintering of the catalyst. Even in the case of a CPO process, the temperature at the catalyst surface may rise upto about 1300° C. due to the highly exothermic hydrocarbon combustion reactions, causing heavy sintering, and consequently deactivation of the catalyst. Hence, the catalyst used in both the processes should have high temperature stability; it should be catalytically active when calcined at a temperature of 1300° C.-1400° C. and also when subjected to high temperature shocks.
A few noble metal or nickel containing catalysts have been claimed in the prior art for their use in the ATR process.
In U.S. Pat. Nos. 4,415,484 and 4,473,543, Setzer et al disclose a Rh deposited on a calcium oxide impregnated alumina, as highly active steam reforming catalyst for use in ATR processes. A rhodium, iridium, palladium, platinum or nickel supported on lanthanum stabilized alumina or magnesium promoted lanthanum stabilized alumina has also been disclosed as highly active, sulphur tolerant steam reforming catalyst useful for the ATR in U.S. Pat. Nos. 4,503,029 and 4,755,498 by Setzer, et. al. However, the use of noble metal containing catalysts in the ATR process is limited because of the high cost of the noble metals used in the catalysts and also because of heavy sintering of the noble metals, leading to catalyst deactivation under the high temperature conditions prevailing in the ATR. The use of nickel containing catalyst in the ATR is also limited because of the solid-solid reaction between the compounds of nickel and alumina leading to formation of catalytically inactive binary metal oxides e.g. nickel aluminates, along with the catalyst sintering under the prevailing high temperature conditions in the ATR (Choudhary et. al. Journal of Catalysis, vol. 172, pages 281-293, year 1997).
Choudhary et al disclose a highly active catalyst, nickel supported on commercial low surface area porous silica-alumina catalyst carrier precoated with magnesia, for oxidative conversion of methane by oxygen to syngas. However, when this catalyst was calcined at 1200° C., it was found to be completely deactivated for the oxidative conversion of methane due to formation of catalytically inactive nickel aluminates by a solid-solid reaction between nickel and alumina from the support and also due to sintering of nickel at the high calcination temperature. The catalyst was however highly active upto its calcination temperature of 1050° C. (Choudhary et al, Journal of Catalysis, vol. 172, pages 281-293, 1997). Hence, use of this catalyst for the ATR or adiabatic CPO processes is limited because of its low temperature stability or deactivation under high temperature operation.
The ATR and CPO processes would become commercially feasible and also attractive provided a robust high temperature stable catalyst, which contains non-noble metal(s) as an active catalyst component(s) and which shows high activity for hydrocarbon(s)-to-syngas conversion when heated to a high temperature, about 1400° C., and also when subjected to high temperature shocks, without its disintrigration, is developed.